Impairment and Disposal of Long-Lived Assets - Assets Held for Sale (Details) $ in Thousands	Jun. 30, 2019 USD ($)	Jun. 30, 2019 a	Jun. 30, 2019 properties	Jun. 30, 2019 bldg	Dec. 31, 2018 USD ($)
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Total assets held for sale	$ 386,726				$ 502,207
Liabilities held for sale	19,033				21,131
Included in Continuing Operations
Balance Sheet Disclosures by Disposal Groups [Line Items]
Number of buildings (in buildings) | bldg				3
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Land and land improvements	3,056				1,301
Buildings and improvements	25,119				5,638
Disposal Group, Including Discontinued Operation, Development in Progress	0				0
Land held for development	21,120				26,253
Accumulated depreciation	(6,559)				(1,546)
Deferred financing and leasing costs, net	1,099				58
Other assets	1,153				164
Total assets held for sale	44,988				31,868
Liabilities held for sale	2,941				141
Included in Discontinued Operations
Balance Sheet Disclosures by Disposal Groups [Line Items]
Number of buildings (in buildings) | bldg				14
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Land and land improvements	91,677				113,080
Buildings and improvements	253,295				384,737
Disposal Group, Including Discontinued Operation, Development in Progress	10,269				9,597
Land held for development	0				0
Accumulated depreciation	(36,946)				(70,242)
Deferred financing and leasing costs, net	10,848				13,697
Other assets	12,595				19,470
Total assets held for sale	341,738				470,339
Liabilities held for sale	16,092				20,990
Total
Balance Sheet Disclosures by Disposal Groups [Line Items]
Acres of Developable Land (in acres) | a		86.0
Number of buildings (in buildings)			4	17
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Land and land improvements	94,733				114,381
Buildings and improvements	278,414				390,375
Disposal Group, Including Discontinued Operation, Development in Progress	10,269				9,597
Land held for development	21,120				26,253
Accumulated depreciation	(43,505)				(71,788)
Deferred financing and leasing costs, net	11,947				13,755
Other assets	13,748				19,634
Total assets held for sale	386,726				502,207
Liabilities held for sale	$ 19,033				$ 21,131